Transducer arrangement for measuring blood flow

ABSTRACT

Perivascular transducer whose piezoelectric plate is bordered on one side thereof by a reflecting and/or absorbing mass and which is equipped with two plastic bands adapted to form a collar around the vessel which is intended to be subjected to the measurement.

United States Patent Peronneau et al.

[451 May 9,1972

[54] TRANSDUCER ARRANGEMENT FOR MEASURING BLOOD FLOW [72] Inventors:Pierre Peronneau, Paris; Fernand Leger,

Gif-sur-Yvette, both of France [73] Assignees: Compagnie GeneraleDElectricite, Paris; Agence Nationale de Valorisation de la Recherche(Anvar), Recherche (Anvar), France 22 Filed: Dec.3l,l969

211 Appl. No.: 889,401

[30] Foreign Application Priority Data Dec. 31, 1968 France ..183135[52] US. Cl. ..l28/2.05 F, 73/67.8, 128/2 V, 310/82 [51] Int.CI. ..A6lb5/02 [58} Field of Search ..128/2.05 F, 2.05 V, 2.05 P, l28/2.05 N, 2.05A, 2.05 R, 2.06 E, 24 A, 2 V;

73/194 A, 67.8; 340/8 RT, 8 MM; 310/82 [56] References Cited UNITEDSTATES PATENTS 3,376,438 4/1968 Colbert ..310/8 2 3,430,625 3/1969McLeod, Jr. 128/205 F 3,443,433 5/1969 Liston et a1. ..73/194 3,387,6046/1968 3,409,869 1 1/1968 McCool et al. 340/8 MM 2,913,602 11/1959 Joy..310/8.3 3,403,271 9/1968 Lobdell et a1. 31.0/8.2 2,946,904 7/1960Renaut .310/8.2 3,270,330 8/1966 Weinberg .310/8.2 3,178,681 4/1965Horsman et al.. ..310/8.2 2,984,756 5/1961 Bradfield ..340/8 MM FOREIGNPATENTS OR APPLICATIONS 166,108 11/1964 U.S.S.R ..l28/2.06

OTHER PUBLICATIONS Herrick, .1. F. et al., IRE Transactions on MedicalElectronics, 1959, pp. 195- 204 Timm, G. W., et al., IEEE Transactionson Bio-Medical Engineering, Oct., 1970, p. 352

Biotronex Laboratory Catalogue, Man, 24, 1967, 4 pages PrimaryExaminer-Richard A. Gaudet Assistant E.\'aminerKyle L. HowellAttorneyCraig, Antonelli, Stewart and Hill 57] ABSTRACT Perivasculartransducer whose piezoelectric plate is bordered on one side thereof bya reflecting and/or absorbing mass and which is equipped with twoplastic bands adapted to form a collar around the vessel which isintended to be subjected to the measurement.

1 Claim, 2 Drawing Figures TRANSDUCER ARRANGEMENT FOR MEASURING BLOODFLOW The present invention relates to a transducer of the piezoelectrictype which is designed for measuring the speed and flow of blood byultrasonic probing or examination. It is known that blood flow can bemeasured with extreme accuracy by the measurement of ultrasonic wavesbackscattered from moving interfaces since such waves exhibit thefamiliar Doppler shift in frequency which has been used for many yearsto detect velocity in other fields. Since blood is one of the mosteffective backscattering media, ultrasonic blood flow velocity sensorshave been found to be most advantageous for diagnosis of certainproblems.

Already known in the art are ultrasonic pick-up and receivinginstruments of this type comprising a small plate made frompiezoelectric ceramic material, enclosed within, or covered by, aplastic material, which is connected to electrical detection apparatusby means of two conductors connected respectively to two surfaces of thesmall piezoelectric plate and adapted to transmit either excitationcurrents to the plate when the latter is operative as an ultrasonicemitter, or currents delivered by the plate operating as an echoreceiver.

In order to obtain the greatest possible sensitivity of such atransducer, it is indispensable that only a single one of the surfacesthereof be acoustically coupled to the propagation medium and subjectedto expansions or vibrations with respect to the opposite surface, whichlatter surface must be removed as much as possible from any mechanicalexcitation. In fact, if the two surfaces must become excited, the idealcondition would be a symmetrical excitation, yet this is a conditionwhich is impossible to attain in a simple and reliable manner. Ratherone would find in practice variable phases on the two surfaces, andhence a reduced sensitivity and nonreproducible or measurable resultswould be provided by the transducer.

It is important, therefore, that the acoustic transmission be made asperfectly as possible between one surface of the plate which is turnedtoward the propagation medium and that, by contrast, the other surfacebe disengaged acoustically from the propagation medium as completely aspossible.

This is the reason why, in accordance with the present invention, in adevice for measuring blood flow comprising a piezoelectric ceramicplate, one of the surfaces of the plate which is not turned toward thepropagation medium is in contact with a mass of material assuring anacoustic disengagement with respect to the propagation medium.

According to another characteristic of the present invention, this massis, or consists of, a material having properties of partial absorptionand partial reflection, for example rubber, foam rubber, or the like.

According to a further characteristic of the present invention, thismass is, or consists of, a material having an almost total absorptionproperty, for example resin charged with metallic particles, or thelike.

According to yet another characteristic of the present invention, thepiezoelectric plate is fixed at or secured to, the end of a catheter andthe mass is placed against the surface of the plate which is turnedtoward the inside of the catheter.

According to a still further characteristic of the present invention, ina perivascular device comprising a cap open toward the propagationmedium, the piezoelectric plate is enclosed with a material assuring agood acoustic transmission on the surface which is turned toward theopening, whereas the opposite surface thereof is in contact with a ballmade from a material such as described above assuring an acousticdisengagement with respect to the propagation medium and provided at thebottom of this cap.

According to another characteristic of the present invention, aperivascular device formed in a cap is glued onto a band of fabric, forexample Dacron, the band having two parts that are aligned on both sidesof the opening of the cap for securing the cap to the vessel to bemonitored.

The present invention will be further described hereinafter withreference to the accompanying drawing, wherein FIG. 1 is across-sectional view, on an enlarged scale, relative to one embodimentof a device according to the present invention, which is mounted at theend of a catheter, and

FIG. 2 is a cross-sectional view of a perivascular device according tothe present invention.

In FIG. 1, a catheter 10 is provided at the end thereof with apiezoelectric plate 11, the surface of which turned toward the inside ofthe catheter 10 is in contact with a mass formed from resilient material12, for example rubber. The catheter 10 contains a coaxial cable 13whose outer conductor 14 is connected to one of the surfaces of theplate 11 by means of a wire 16, and the inner conductor 15 thereof isconnected to the other surface of the plate 11 by means of a wire 17.The coaxial cable 13 is advantageously made stationary within thecatheter 10 by means of an epoxy resin 18. A varnish film 19 covers thesurface in front of the ceramic plate 11.

The piezoelectric ceramic plate 11 may also be inclined, if desired,with respect to the axis of the catheter; this will allow for thesensitive field or radiation field of the ceramic material to cover thesection of the vessel without resorting to a centering device.

Looking now to FIG. 2, which illustrates an embodiment forming aperivascular device, disposed in a stationary manner within a cap 20 isa piezoelectric ceramic plate 21 between a rubber mass in the form of aball 22 in the bottom of this cap and a plastic mass 23, which may beany suitable material, for example the material known by the nameALTUGLAS, facing toward the opening of the cap. This opening is equippedor provided over the entire extension thereof with a sole 24 also madefor example from ALTUGLAS which may be plated against the wall 30 of avessel intended to be subjected to a measurement. The elements 20, 23,24 may also constitute a single mass or unitary structure.

In certain cases, the impedance match with the vascular wall is assuredby means of a mass of gel (not shown) placed upon the emitting surfaceof the ceramic plate 21.

The fixing of the transducer on the vessel is advantageouslyaccomplished with the aid of two portions of a band, for example madefrom Dacron, on which the transducer is fixed, for example by gluing.One of these portions or strands is visible at 25 passing in front ofthe vessel, and the other one is visible at 26 returning from behind thevessel. In order to assure the connection with the vessel, the twoportions are sutured together at 27 and 28, thus forming a sort ofbracelet around the vessel.

This particular form of construction is very advantageous since itallows for establishing the connection between the pick-up and thevessel with the smallest traumatization possible. On a band one may fixeither a single pick-up device or transducer which serves alternately asemitter and as receiver, or two pick-up devices, being specific to eachfunction.

Although the present invention has been described with reference to buta single embodiment, it is to be understood that the scope of theinvention is not limited to the specific details thereof, but issusceptible of numerous changes and modifications as would be apparentto one with normal skill in the pertinent technology.

What we claim is:

l. Perivascular transducer arrangement comprising at least onetransducer mounted within a cap open at one side and being formed by apiezoelectric plate, a body formed of a first material assuring a goodacoustic transmission being disposed between one side of saidpiezoelectric plate and the opening of the cap, the opposite side ofsaid plate within the cap being in contact with a body of materialproviding acoustic disengagement with respect to acoustic waves directedto said one side of said plate, said cap being secured to a band havingtwo portions aligned on respective sides of the opening of the cap andadapted to be closed in the form of a collar around a vessel, electricallead means extending through said cap and connected to saidpiezoelectric plate, said first material being a plastic mass and saidmaterial providing acoustic dis-engagement being a partial reflector andpartial absorber of acoustic waves. a n it

1. Perivascular transducer arrangement comprising at least onetransducer mounted within a cap open at one side and being formed by apiezoelectric plate, a body formed of a first material assuring a goodacoustic transmission being disposed between one side of saidpiezoelectric plate and the opening of the cap, the opposite side ofsaid plate within the cap being in contact with a body of materialproviding acoustic disengagement with respect to acoustic waves directedto said one side of said plate, said cap being secured to a band havingtwo portions aligned on respective sides of the opening of the cap andadapted to be closed in the form of a collar around a vessel, electricallead means extending through said cap and connected to saidpiezoelectric plate, said first material being a plastic mass and saidmaterial providing acoustic dis-engagement being a partial reflector andpartial absorber of acoustic waves.